Diana M. Rankin is a master gardener, a professional writer and a member of Grants Professional Association.

This article applies to:



Plant Selection Key to Reducing Allergies
by Diana M. Rankin       #Health and Safety   #Spring   #Weather

Common ragweed is one of the most allergenic of all pollen sources, rating a 10 on OPALS. It is an annual weed and should be removed from the garden before it blooms.

Do you or does someone you know suffer from seasonal allergies, hay fever or asthma triggered by pollen? Are you tired of watery itchy eyes, a scratchy throat, a runny nose, sneezing and a stuffy head whenever you venture into your backyard? No, this isn’t a commercial for the newest antihistamine or decongestant miracle drug. Instead, it’s about how to have a garden that is virtually allergy-free.


Change in Ragweed Pollen Season (1995-2013)
This map demonstrates how the ragweed allergy season is increasing from south to north. This seems to be caused by a combination of warmer temperatures, later fall frosts and increased carbon dioxide in the air.


Prevalence of Pollen-Related Allergies
In 2013, the American College of Allergy, Asthma and Immunology estimated 16.9 million adults and 6.7 million children were diagnosed with allergic rhinitis, commonly known as hay fever. Seasonal allergic rhinitis is usually caused by sensitivity to tree, grass, weed or other plant pollens.

Common ragweed (Ambrosia artemisiifolia) alone affects an estimated 26 percent of all Americans. A single ragweed plant can produce up to 1 billion pollen grains in a season and these are carried long distances by the wind. The ragweed season is getting longer in many parts of the country. “Warmer temperatures and later fall frosts allow ragweed plants to produce pollen later into the year, potentially prolonging the allergy season for millions of people,” said a 2014 Environmental Protection Agency report. Furthermore, higher levels of carbon dioxide in the atmosphere stimulate plant growth, leading to more overall pollen production. We can look forward to longer, possibly more severe, hay fever seasons triggered by all kinds of wind-borne pollen.

What’s a Gardener to Do?
Avoidance is the key in allergy relief, wrote Thomas Leo Ogren in his book, Allergy-Free Gardening, (Berkeley, TenSpeed Press. 2000). Here are some suggestions:

• Eliminate allergy-causing plants in your yard and avoid exposure to those plants elsewhere.
• Don’t plant allergy-triggering plants near the home or garage entryways.
• Stay away from plants with pollen carried by the wind. This includes ragweed and several tree species.
• Remove ragweed and related weeds, such as pigweed (Amaranthus palmeri) and lamb’s quarters (Chenopodium album) before the flowers appear.
• Avoid being outdoors between 5 and 10 a.m., when the air is most saturated with pollen grains.
• Monitor pollen counts using local weather media and online resources, such as pollen.com, or with a pollen alert app for your smart phone. (For reviews of these apps, visit Healthline.com, bit.ly/1z2KjMq).
• Avoid being outdoors on windy days, especially when pollen counts are high.
• Wear a National Institute for Occupational Safety and Health- or NIOSH- rated, 95-filter mask if pollen counts are high.
• Take medication prior to going outdoors, but only as directed by your allergist.
• Select only garden and landscape plants that will not contribute to pollen allergy symptoms.


‘Boulder Blue’ is a beautiful grass for the perennial border, but blue fescues are rated 9 on OPALS. Do not plant it in your allergy-free garden. • The herb borage has blue flowers, which are a favorite of bumblebees. These are perfect flowers, meaning that both male and female parts are within a single flower. • In the spring, pine trees shed copious amounts of pollen. The OPALS rating, however, is only a 4 because the pollen is waxy and not very irritating to mucous membranes.

Plants for a (Nearly) Allergy-Free Garden
Allergy-Free Gardening is one of the best resources for finding which plants have the greatest allergy potential. Each plant is rated on the Ogren Plant-Allergy Scale, trademarked as OPALS. This scale of 1 to 10 is based on Ogren’s groundbreaking research on the allergy-potential of hundreds of plants, including cultivars of the most allergenic landscape plants. In addition to pollen, the scale considers the potential for contact dermatitis, odor allergy and whether or not a plant is poisonous. A rating of 1 indicates the most allergy-free and 10 the least allergy-free.

There are also some general rules, which Ogren discusses in his book.

• Avoid plants that are pollinated by the wind, rather than insects. Wind-pollinated plants have small, inconspicuous green or brown flowers in dense clusters, and the pollen grains are small, light and dry, so that they can be carried easily by the wind. These include Artemesia species, such as tarragon and wormwood; conifers; spring-blooming deciduous trees; and grasses, especially un-mowed Kentucky bluegrass, zoysia grass, junegrass, timothy and orchard grass.
• Select bright, highly colored, lightly scented flowering plants. These have heavy, sticky pollen that bees and other insects move from flower to flower in the pollination process. Examples are: crab apples (Malus domestica), Petunia, roses (Rosa), Dianthus, daylilies (Hemerocallis hybrids) and Zinnia.







Above: Coralburst Crabapple (Malus ‘Coralcole’)

Right: Penstemon ‘Dark Towers’ is an excellent selection for the allergy-free, perennial border. Tubular pink flowers are insect-pollinated.

Plant Parts and Pollination
Finding out how the male pollen makes its way to the female flower parts is the best way to know a specific plant’s potential for causing allergy symptoms.

• Perfect flowers are those that have both male and female parts inside a single flower. Pollinating insects only need to move the pollen a short distance from flower to flower. Perfect-flowered plants include apples (Malus) and roses.
• Monoecious plants have separate male and female flowers on the same plant. The pollen is transferred from one flower to the other by gravity or by wind. Examples of monoecious plants are corn and oak.
• Dioecious plants are separate-sexed; that is, individual plants in the species are either all male or all female. For pollination to occur, the wind must carry pollen from the male plant to the female. Examples of dioecious plants include ash, willow, poplar, holly and some maples.

Red Sunset is a female red maple selection, thus pollen-free. It was named Iowa Tree of the Year in 2000.

For the allergy-sufferer, perfect-flowered plants are the best choice. Monoecious plants should be avoided along with male dioecious plants. Female dioecious plants are acceptable, but beware that some, such as ginkgo (G. biloba), bear messy or unpleasant fruit. There are also some female-named cultivars, such Red Sunset red maple (Acer rubrum ‘Franksred’), that are excellent choices for the home landscape.

Although it can be challenging to plant a nearly allergy-free garden and landscape, it is definitely possible. You may not be able to plant some of the things you would like to have, but there are many, many others that are good substitutes. As Ogren’s book emphasizes, anyone can have a garden that is very nearly allergy-free through avoidance and careful selection.


A version of this article appeared in a January/February 2015 print edition of State-by-State Gardening.
Photography courtesy of Gardendreamer_Dreamstime.com, Diana M. Rankin, Bailey Nurseries, bendicks/canstockphoto.com, and Van Meuven.


Posted: 02/01/18   RSS | Print


Share this story on:
Facebook       Twitter            

Other People Are Reading